Method of recovering cathode active material precursor

ABSTRACT

A method of recovering a cathode active material precursor according to an embodiment of the present invention includes preparing a cathode active material mixture including a lithium composite oxide, separating lithium from the cathode active material mixture to form a preliminary transition metal precursor, acid-treating the preliminary transition metal precursor to form a complex transition metal salt solution, and adding an acidic extractant to the complex transition metal salt solution and then adding a basic compound to recover a transition metal precursor, and thus the extraction rate of transition metals can be improved.

CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application claims benefit under 35 U.S.C. 119, 120, 121, or365(c), and is a national stage entry from international Application No.PCT/KR2020/017857, filed Dec. 8, 2020, which claims priority to thebenefit of Korean Patent Application No. 10-2019-0175438 filed in theKorean Intellectual Property Office on Dec. 26, 2019, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

The present invention relates to a method of recovering a cathode activematerial precursor. More particularly, the present invention relates toa method of recovering a cathode active material precursor from acathode active material mixture.

2. Background Art

A secondary battery which can be charged and discharged repeatedly hasbeen widely employed as a power source of a mobile electronic devicesuch as a camcorder, a mobile phone, a laptop computer, etc., accordingto developments of information and display technologies. The secondarybattery includes, e.g., a lithium secondary battery, a nickel-cadmiumbattery, a nickel-hydrogen battery, etc. The lithium secondary batteryis highlighted due to high operational voltage and energy density perunit weight, a high charging rate, a compact dimension, etc.

The lithium secondary battery may include an electrode assemblyincluding a cathode, an anode, a separation layer (separator), and anelectrolyte immersing the electrode assembly. The lithium secondarybattery may further include an outer case having, e.g., a pouch shapefor housing the electrode assembly and the electrolyte.

A lithium composite oxide may be used as a cathode active material ofthe lithium secondary battery. The lithium composite oxide mayadditionally contain a transition metal such as nickel, cobalt,manganese, etc.

The lithium composite oxide as the cathode active material may beprepared by reacting a lithium precursor and a nickel-cobalt-manganese(NCM) precursor containing nickel, cobalt and manganese.

As the above-mentioned high-cost valuable metals are used for thecathode active material, 20% or more of a production manufacturing costis required for manufacturing the cathode material. Additionally, asenvironment protection issues have recently been highlighted, arecycling method of the cathode active material is being researched. Forthe recycling of the cathode active material, regeneration of thelithium precursor from a waste cathode is required with high efficiencyand high purity.

For example, Korean Published Patent Application No. 2015-0002963discloses a method for recovering lithium using a wet method. However,lithium is recovered by a wet extraction from a waste liquid remainingafter extraction of cobalt, nickel, etc., and thus a recovery ratio isexcessively reduced and a large amount of impurities may be generatedfrom the waste liquid.

SUMMARY

According to an aspect of the present invention, there is provided amethod of recovering a cathode active material precursor from a cathodeactive material mixture with high purity, high yield and highefficiency.

A method of recovering a cathode active material precursor according toexemplary embodiments of the present invention includes preparing acathode active material mixture including a lithium composite oxide;separating lithium from the cathode active material mixture to form apreliminary transition metal precursor; acid-treating the preliminarytransition metal precursor to form a complex transition metal saltsolution; and adding an acidic extractant to the complex transitionmetal salt solution and then adding a basic compound to recover atransition metal precursor.

In some embodiments, the forming the preliminary transition metalprecursor may include hydrogen-reducing the cathode active materialmixture to form a preliminary precursor mixture, and washing thepreliminary precursor mixture with water to separate lithium.

In some embodiments, the forming the complex transition metal saltsolution may include acid-treating the preliminary transition metalprecursor so that a pH of the complex transition metal salt solution maybe from 0.1 to 2.0.

In some embodiments, the forming the complex transition metal saltsolution may include acid-treating the preliminary transition metalprecursor using sulfuric acid.

In some embodiments, the complex transition metal salt solution maycontain a sulfate of a transition metal complex including at least twotransition metals selected from the group consisting of nickel, cobaltand manganese.

In some embodiments, wherein the acidic extractant may include at leastone selected from the group consisting of a phosphoric acid-basedextractant, a phosphate-based extractant and a phosphine oxide-basedextractant.

In some embodiments, the acidic extractant may further include adiluent.

In some embodiments, the diluent may include at least one selected fromthe group consisting of kerosene, hexane, benzene and toluene.

In some embodiments, the recovering the transition metal precursor mayinclude mixing the complex transition metal salt solution and the acidicextractant so that an organic phase/aqueous phase ratio may be from 2 to10.

In some embodiments, the recovering the transition metal precursor mayinclude adding the basic compound to a mixture of the complex transitionmetal salt solution and the acidic extractant so that an equilibrium pHmay be from 3.5 to 6.

In some embodiments, the basic compound may include at least oneselected from the group consisting of lithium hydroxide, sodiumhydroxide and potassium hydroxide.

According to exemplary embodiments of the present invention, apreliminary transition metal precursor from which a lithium precursor isseparated from a cathode active material mixture may be acid-treated,and then a high-purity transition metal precursor may be obtained inhigh yield and high efficiency using an acidic extractant and a basiccompound.

The transition metal precursor may be recovered after separating thelithium precursor from the cathode active material mixture, so that thetransition metal precursor may be extracted at a high equilibrium pH.Accordingly, a recovery ratio of a transition metal (e.g., nickel) maybe improved.

Additionally, transition metal may not be individually extracted, butmay be extracted in a single batch in the form of a composite transitionmetal precursor.

Accordingly, an extraction efficiency may be improved.

DETAILED DESCRIPTION

According to exemplary embodiments of the present invention, atransition metal precursor may be recovered using an acidic extractantand a basic compound after separating a lithium precursor from thecathode active material mixture in advance, and thus the cathode activematerial precursor may be recovered with high yield and high efficiency.

The term “precursor” in the present application is used tocomprehensively refer to a compound including a specific metal toprovide the specific metal included in an electrode active material.

In a method of recovering a cathode active material precursor accordingto some embodiments, a cathode active material mixture including alithium composite oxide may be prepared.

In exemplary embodiments, the cathode active material mixture may beobtained from a waste lithium secondary battery. The waste lithiumsecondary battery may include a lithium secondary battery that may notbe reused (charge/discharge) substantially. For example, the wastelithium secondary battery may be a lithium secondary battery from whicha charge/discharge efficiency is greatly reduced due to a termination ofa life-span, or a lithium secondary battery destroyed by a shock or achemical reaction.

The waste lithium secondary battery may include, e.g., an electrodeassembly including a cathode, an anode and a separation layer interposedbetween the cathode and the anode. For example, the cathode and theanode may include a cathode active material layer and an anode activematerial layer coated on the cathode current collector and the anodecurrent collector, respectively.

For example, the cathode active material included in the cathode activematerial layer may include an oxide containing lithium and a transitionmetal.

In some embodiments, the cathode active material may be an NCM-basedlithium oxide including nickel, cobalt and manganese. However,embodiments of the present invention may be commonly applied to acathode material including the NCM-based lithium oxide and alithium-containing cathode material.

For example, a waste cathode may be recovered by separating the cathodefrom the waste lithium secondary battery. The cathode may include thecathode current collector (e.g., aluminum (Al)) and the cathode activematerial layer as described above, and the cathode active material layermay include a conductive material and a binder together with theabove-described cathode active material.

The conductive material may include, e.g., a carbon-based material suchas graphite, carbon black, graphene, carbon nanotube, etc. The bindermay include a resin material, e.g.,vinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP),polyvinylidenefluoride (PVDF), polyacrylonitrile,polymethylmethacrylate, etc.

For example, the cathode active material mixture may be prepared fromthe recovered cathode. The term “cathode active material mixture” asused herein refers to a mixture in which a cathode current collectorcomponent such as aluminum is substantially completely separated andremoved from the recovered cathode, and a content of carbon-basedcomponents derived from the conductive material and the binder isremoved or reduced.

In some embodiments, the cathode active material mixture may be obtainedin the form of a powder by a physical treatment such as pulverizationtreatment of the recovered cathode. As described above, the cathodeactive material mixture may include a lithium-transition metal oxidepowder, e.g., an NCM-based lithium oxide powder (e.g., Li(NCM)O₂).

In some embodiments, the recovered cathode may be heat-treated beforethe pulverization treatment. Accordingly, during the pulverizationtreatment, detachment of the cathode current collector may befacilitated, and the binder and the conductive material may be at leastpartially removed. A temperature of the heat treatment may be, e.g.,from about 100 to 500° C., preferably from about 350 to 450° C.

In some embodiments, the cathode active material mixture may be obtainedafter immersing the recovered cathode in an organic solvent. Forexample, the recovered cathode may be immersed in an organic solvent toseparate and remove the cathode current collector, and the cathodeactive material mixture may be selectively extracted through acentrifugation.

Through the above-described processes, the cathode active materialmixture from which the contents of the cathode current collectorcomponent and the carbon-based component derived from the conductivematerial and/or the binder are substantially removed or reduced may beachieved.

The cathode active material mixture may include, e.g., alithium-containing compound used in a cathode active material of anelectrochemical device. For example, a lithium composite oxide may beused as the cathode active material mixture.

For example, the lithium composite oxide may include lithium and atransition metal. The transition metal may include, e.g., nickel,cobalt, manganese, or the like.

In some embodiments, the lithium composite oxide may be represented byChemical Formula 1 below.

Li_(x)Ni_(a)Co_(b)M_((1-a-b))O_(y)  [Chemical Formula 1]

In Chemical Formula 1, M may be selected from the group consisting ofMn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Gaand B, and 0<x≤1.1 , 2≤y≤2.02, 0.5≤a≤1, 0≤b≤0.5.

In exemplary embodiments, a lithium composite oxide having a Ni contentof 0.5 molar ratio or more may be effectively converted into a lithiumcomposite oxide.

The cathode active material mixture may further include variouslithium-containing compounds such as lithium oxide, lithium carbonate,lithium hydroxide as a non-limiting example.

In some embodiments, lithium may be separated from the prepared cathodeactive material mixture to form a preliminary transition metalprecursor. For example, lithium may be separated from the cathode activematerial mixture in the form of lithium oxide or lithium hydroxide.

In exemplary embodiments, the formation of the preliminary transitionmetal precursor may include reducing the cathode active material mixtureto form a preliminary precursor mixture, and washing the preliminaryprecursor mixture with water to separate lithium.

For example, a hydrogen reduction treatment of the preliminary cathodeactive material mixture may be performed to form the preliminaryprecursor mixture, and then the preliminary precursor mixture may bewashed with water to separate a lithium precursor including lithiumhydroxide.

In some embodiments, the hydrogen reduction treatment may be performedusing a fluidized bed reactor. For example, the cathode active materialmixture may be introduced into the fluidized bed reactor and a hydrogengas may be injected from a bottom portion of the fluidized bed reactor.

A cyclone may be formed from the bottom portion of the fluidized bedreactor by the hydrogen gas, and the preliminary precursor mixture maybe generated while the cathode active material mixture and hydrogencontact each other.

In some embodiments, a carrier gas and the hydrogen gas may be mixed andinjected at the bottom portion of the fluidized bed reactor.Accordingly, a gas-solid mixing may be promoted to enhance a reaction ina fluidized bed, and a reaction layer of the preliminary precursormixture in the fluidized bed reactor may be easily formed.

The carrier gas may include, e.g., an inert gas such as nitrogen (N₂) orargon (Ar).

The preliminary precursor mixture may include, e.g., a hydrogenreductive product of a lithium-transition metal oxide included in thecathode active material mixture. If the NCM-based lithium oxide is usedas the lithium-transition metal oxide, the preliminary precursor mixturemay include a preliminary lithium precursor and a preliminary transitionmetal precursor.

The preliminary lithium precursor may include lithium hydroxide, lithiumoxide and/or lithium carbonate.

A transition metal component of the preliminary transition metalprecursor may be derived from the lithium composite oxide in therecovered cathode. For example, in a reaction in which the lithiumcomposite oxide is converted into lithium oxide, the transition metalcomponent may be separated to form the preliminary transition metalprecursor. The preliminary transition metal precursor may include, e.g.,Ni, Co, NiO, CoO, MnO, or the like.

The hydrogen reductive reaction may be performed at a temperature fromabout 400 to 700° C., preferably from about 450 to 550° C.

The preliminary lithium precursor may be converted into a lithiumprecursor substantially consisting of lithium hydroxide by the washingtreatment. For example, lithium oxide and lithium carbonate mixed in thepreliminary lithium precursor may be converted into lithium hydroxide bybeing reacted with water, or may be removed by the washing treatment.Accordingly, a high-purity lithium precursor converted into a desiredlithium hydroxide form may be produced.

The preliminary lithium precursor may be dissolved by being reacted withwater to substantially prepare an aqueous lithium hydroxide solution.

The preliminary transition metal precursor included in the preliminaryprecursor mixture may be precipitated without being dissolved or reactedin water by the washing treatment. Thus, a lithium precursor includingthe high-purity lithium hydroxide may be obtained and separated from thepreliminary transition metal precursor by a filtration.

In some embodiments, the washing treatment may be performed under acondition from which carbon dioxide (CO₂) is excluded. For example, thewashing treatment may be performed in a CO₂-free atmosphere (e.g., anair atmosphere from which CO₂ is removed), so that regeneration oflithium carbonate may be prevented.

In an embodiment, water provided during the washing treatment may bepurged (e.g., nitrogen purged) using a CO₂ deficient gas to create theCO₂-free atmosphere.

In some embodiments, the preliminary transition metal precursor may betreated with an acid to form a complex transition metal salt solution.For example, the complex transition metal salt solution may be an acidsalt solution in which the preliminary transition metal precursor andthe acid are reacted, and may include a complex transition metal sulfatesolution when sulfuric acid is used.

For example, the complex transition metal salt solution may includenickel, cobalt or manganese. For example, the complex transition metalsalt solution may refer to an acid salt solution of a complex of two ormore transition metals selected from the group consisting of nickel,cobalt and manganese.

In exemplary embodiments, the acid treatment may be performed for about60 to 500 minutes by putting the preliminary transition metal precursorin a sulfuric acid solution at a temperature from about 50 to 90° C. Forexample, an average pH of the complex transition metal salt solutionformed by the acid treatment may be from about 0.1 to 2.0. Within theabove ranges of the temperature, the time, and the pH, the complextransition metal salt solution may be more easily formed. Further, anextraction efficiency of the transition metal may be improved.

For example, a solid-liquid ratio of the acid used for acid treatment ofthe preliminary transition metal precursor may be about 140 g/L or less.More preferably, the solid-liquid ratio may be from about 90 g/L to 130g/L.

For example, a concentration of the acid used for acid treatment of thepreliminary transition metal precursor may be about 1.8 M or more. Morepreferably, the concentration of the acid may be from about 1.8 M to 10M.

Within the ranges of the solid-liquid ratio and the acid concentration,the complex transition metal salt solution may be formed withoutaddition of a redox agent. Accordingly, a high-purity transition metalcomplex may be recovered with high efficiency.

In some embodiments, the complex transition metal precursor may berecovered by adding an acidic extractant to the complex transition metalsalt solution, and then adding a basic compound.

In some exemplary embodiments, the acid extractant may include at leastone selected from the group consisting of a phosphoric acid-basedextractant, a phosphate-based extractant, and a phosphine oxide-basedextractant.

For example, the acidic extractant may include at least one selectedfrom the group consisting of di-2-ethylhexyl phosphoric acid,bis(2,4,4-trimethylpentyl) phosphinic acid, bis(2,4,4-trimethylpentyl)dithiophosphinic acid, 2-ethylhexyl phosphoric acid mono-2-ethylhexylester, tributyl phosphate and trioctyl phosphine oxide. More preferably,the acidic extractant may include di-2-ethylhexyl phosphoric acid. Forexample, the acid extractant may improve a ratio of extracting thetransition metal (e.g., a transition metal extraction ratio) from thecomplex transition metal salt solution.

In some exemplary embodiments, the acid extractant may further include adiluent. For example, the diluent may be an organic solvent. Forexample, the organic solvent may include at least one selected from thegroup consisting of kerosene, hexane, benzene and toluene. Morepreferably, the organic solvent may include kerosene.

In some exemplary embodiments, the complex transition metal saltsolution and the acid extractant may be mixed so that a ratio of anorganic phase to an aqueous phase (organic phase/aqueous phase) is from2 to 10. More preferably, the complex transition metal salt solution andthe acid extractant may be mixed so that the ratio of the organicphase/the aqueous phase is from 3 to 7. For example, within the ratio ofthe organic phase and the aqueous phase, the organic phase/aqueous phaseratio may be appropriate so that a separation efficiency of the complextransition metal precursor extracted per unit time may be furtherimproved.

In some exemplary embodiments, the basic compound may be added to themixture so that an equilibrium pH of the mixture of the complextransition metal salt solution and the acidic extractant may be fromabout 3.5 to 6. For example, lithium has already been separated in thecomposite transition metal salt solution and a content of lithium isreduced, so that the transition metal extraction may be performed in arelatively high pH range. Accordingly, an extraction ratio for thetransition metals, particularly nickel and cobalt, may be improved.

For example, when the equilibrium pH of the mixture of the complextransition metal salt solution and the acidic extractant is less thanthe above-mentioned equilibrium pH range, the extraction ratio of thetransition metal may be degraded.

For example, if the equilibrium pH of the mixture of the complextransition metal salt solution and the acidic extractant exceeds theabove-mentioned range, a side reaction such as a metal precipitation mayoccur. Further, as the average pH of the complex transition metal saltsolution increases, a loading amount of the metal in the organic phasemay increase, thereby increasing a density and a viscosity of thesolution. Accordingly, a fluidity of the organic phase may be reduceddue to the high density and high viscosity of the solution, and anefficiency of a phase separation from the aqueous phase may be degraded.

In some exemplary embodiments, the basic compound may include at leastone selected from the group consisting of lithium hydroxide, sodiumhydroxide and potassium hydroxide.

For example, a percent concentration of the basic compound may be fromabout 10 to 60%. Within the range of the percent concentration of thebasic compound, the equilibrium pH of the mixture of the complextransition metal salt solution and the acidic extractant may befacilitated may be easily adjusted.

In exemplary embodiments, a cathode active material precursor may beprepared, and a transition metal hydroxide may be obtained through anappropriate treatment for the cathode active material precursor, whichmay be used to prepare a cathode active material.

Hereinafter, preferred embodiments are proposed to more concretelydescribe the present invention. However, the following examples are onlygiven for illustrating the present invention and those skilled in therelated art will obviously understand that these examples do notrestrict the appended claims but various alterations and modificationsare possible within the scope and spirit of the present invention. Suchalterations and modifications are duly included in the appended claims.

Example 1

1 kg of a cathode material recovered from a waste lithium secondarybattery was heat-treated at 450° C., cut into subunits and pulverized bya milling. The pulverized cathode material was filtered through an 80μm-mesh sized sieve to remove a cathode current collector component (Al)and carbon-based impurities to obtain a cathode active material mixture.

10 g of the cathode active material mixture was charged in a column-typehydrogen reduction reactor, 20% hydrogen gas was injected, and themixture was reacted at 450° C. for 2 hours to obtain a preliminaryprecursor mixture.

The preliminary precursor mixture was reacted with 100 ml ofnitrogen-purged water, filtered through a filter paper and alithium-containing supernatant and a preliminary transition metalprecursor-containing precipitate were obtained by a centrifugation.

After removing the lithium-containing supernatant, the preliminarytransition metal precursor-containing precipitate was dried. 130 g ofthe dried precipitate was added to 1 L of 2 mol/L sulfuric acid to forma complex transition metal salt solution. A pH of the obtained complextransition metal salt solution was 0.11.

An acidic extractant containing 1 mol/L of di-2-ethylhexyl phosphoricacid and kerosine was added to the complex transition metal saltsolution to form a mixture of the complex transition metal salt solutionand the acidic extractant. An organic/aqueous phase ratio of the mixturewas 6. Thereafter, sodium hydroxide having a percent concentration of50% was added to the mixture and an equilibrium pH of the mixture wasadjusted to 4.74 to extract a complex transition metal precursor.

Examples 2 to 8

A complex transition metal precursor was extracted by the same method asthat in Example 1, except that the equilibrium pH and the organicphase/aqueous phase ratio of the mixture of the complex transition metalsalt solution and the acidic extractant were adjusted as shown in Table1 below.

Comparative Example 1

1 kg of a cathode material recovered from a waste lithium secondarybattery was heat-treated at 450° C., cut into subunits, and pulverizedby a milling. The pulverized cathode material was filtered through an 80μm-mesh sized sieve to remove a cathode current collector component (Al)and carbon-based impurities to obtain a cathode active material mixture.

200 g of the cathode active material mixture was added to 1 L of 3 mol/Lsulfuric acid, and 10 vol % of H₂O₂ having a percent concentration of35% as a reducing agent was added relative to an amount of sulfuric acidto form a complex transition metal salt solution. A pH of the complextransition metal salt solution was 0.48.

An acidic extractant containing 1 mol/L of di-2-ethylhexyl phosphoricacid and kerosine was added to the complex transition metal saltsolution to form a mixture of the complex transition metal salt solutionand the acidic extractant. An organic/aqueous phase ratio of the mixturewas 6. Thereafter, sodium hydroxide having a percent concentration of50% was added to the mixture and an equilibrium pH of the mixture wasadjusted to 4.7 to extract a complex transition metal precursor.

Comparative Examples 2 to 4

A complex transition metal precursor was extracted by the same method asthat in Comparative Example 1, except that the equilibrium pH and theorganic phase/aqueous phase ratio of the mixture of the complextransition metal salt solution and the acidic extractant were adjustedas shown in Table 1 below.

TABLE 1 organic/aqueous No. phase ratio equilibrium pH Example 1 6 4.7Example 2 6 3.8 Example 3 6 3.2 Example 4 6 2.5 Example 5 6 6.1 Example6 1 4.7 Example 7 2 4.7 Example 8 10 4.7 Comparative Example 1 6 4.7Comparative Example 2 6 3.6 Comparative Example 3 6 3.4 ComparativeExample 4 6 2.3

Experimental Example: Calculation of Metal Extraction Ratio

An extraction ratio was calculated by comparing a weight percent of thetransition metals present in the aqueous phase before and after theextraction. Weight percents of the transition metals present in theaqueous phase before and after extraction and the extraction ratecalculated therefrom are shown in Table 2 below.

TABLE 2 aqueous phase aqueous phase before extraction (wt %) afterextraction (wt %) extraction ratio (%) No. Mn Co Ni Li Mn Co Ni Li Mn CoNi Li Example 1 0.7 0.8 5.9 0.2 0.01 0.1 1.4 0.1 99 87 76 50 Example 20.7 0.8 5.9 0.2 0.01 0.2 2.8 0.1 99 75 53 50 Example 3 0.7 0.8 5.9 0.20.01 0.3 3.6 0.1 99 62 39 50 Example 4 0.7 0.8 5.9 0.2 0.02 0.5 4.2 0.197 38 29 50 Example 5 0.7 0.8 5.9 0.2 0.01 0.05 1.1 0.1 99 94 81 50Example 6 0.7 0.8 5.9 0.2 0.03 0.68 5.6 0.2 96 15 5 0 Example 7 0.7 0.85.9 0.2 0.02 0.43 4.9 0.18 97 46 17 10 Example 8 0.7 0.8 5.9 0.2 0.010.03 0.6 0.06 99 96 90 70 Comparative 0.7 0.9 6.6 1.0 0.01 0.2 2.9 0.699 78 56 40 Example 1 Comparative 0.7 0.9 6.6 1.0 0.01 0.3 4.1 0.6 99 6738 40 Example 2 Comparative 0.7 0.9 6.6 1.0 0.01 0.5 4.8 0.6 99 44 27 40Example 3 Comparative 0.7 0.9 6.6 1.0 0.04 0.6 4.9 0.6 94 33 25 40Example 4

Referring to Table 2 above, as the organic phase/aqueous phase ratioincreased, the number of sites in which the metal present in the organicphase could be extracted increased, and thus the extraction ratio of themetal was increased.

Referring to Example 5, when the average pH of the mixture of thecomplex transition metal salt solution and the acidic extractantexceeded 6.0, an amount of extracted metal increased, thereby increasinga viscosity and a density of the extractant.

Accordingly, a separation from the aqueous phase was difficult.

Referring to Table 2, when the organic phase/aqueous phase ratio of thecomplex transition metal salt solution, the acidic extractant and thebasic compound was from 2 to 10, and the equilibrium pH range was from3.5 to 6, the extraction ratio of the transition metal was furtherimproved.

1. A method of recovering a cathode active material precursor,comprising: preparing a cathode active material mixture including alithium composite oxide; separating lithium from the cathode activematerial mixture to form a preliminary transition metal precursor;acid-treating the preliminary transition metal precursor to form acomplex transition metal salt solution; and adding an acidic extractantto the complex transition metal salt solution and then adding a basiccompound to recover a transition metal precursor.
 2. The method ofrecovering a cathode active material precursor of claim 1, wherein theforming the preliminary transition metal precursor compriseshydrogen-reducing the cathode active material mixture to form apreliminary precursor mixture, and washing the preliminary precursormixture with water to separate lithium.
 3. The method of recovering acathode active material precursor of claim 1, wherein the forming thecomplex transition metal salt solution comprises acid-treating thepreliminary transition metal precursor so that a pH of the complextransition metal salt solution is from 0.1 to 2.0.
 4. The method ofrecovering a cathode active material precursor of claim 1, wherein theforming the complex transition metal salt solution comprisesacid-treating the preliminary transition metal precursor using sulfuricacid.
 5. The method of recovering a cathode active material precursor ofclaim 4, wherein the complex transition metal salt solution contains asulfate of a transition metal complex including at least two transitionmetals selected from the group consisting of nickel, cobalt andmanganese.
 6. The method of recovering a cathode active materialprecursor of claim 1, wherein the acidic extractant comprises at leastone selected from the group consisting of a phosphoric acid-basedextractant, a phosphate-based extractant and a phosphine oxide-basedextractant.
 7. The method of recovering a cathode active materialprecursor of claim 1, wherein the acidic extractant further comprises adiluent.
 8. The method of recovering a cathode active material precursorof claim 7, wherein the diluent comprises at least one selected from thegroup consisting of kerosene, hexane, benzene and toluene.
 9. The methodof recovering a cathode active material precursor of claim 1, whereinthe recovering the transition metal precursor comprises mixing thecomplex transition metal salt solution and the acidic extractant so thatan organic phase/aqueous phase ratio is from 2 to
 10. 10. The method ofrecovering a cathode active material precursor of claim 1, wherein therecovering the transition metal precursor comprises adding the basiccompound to a mixture of the complex transition metal salt solution andthe acidic extractant so that an equilibrium pH is from 3.5 to
 6. 11.The method of recovering a cathode active material precursor of claim10, wherein the basic compound comprises at least one selected from thegroup consisting of lithium hydroxide, sodium hydroxide and potassiumhydroxide.